In-situ exfoliation and integration of vertically aligned graphene for high-frequency response on-chip microsupercapacitors

Abstract

Fast response on-chip micro-supercapacitors (MSCs) with large energy storage capabilities are highly in demand for high-frequency circuits and systems such as alternating current (AC) line filters. Devices with vertically aligned graphene thin-film electrodes were shown to be promising in maintaining close-to-ideal capacitive behavior at high frequencies due to low ionic and electric resistances. This study investigates a novel in-situ integration of vertically aligned graphene layers with micro-sized gold current collectors in which a modified bipolar electrochemistry method has been applied. The electrochemical analysis revealed a high average capacitance of 640 μF cm−2 (C.V−1cm−2) at a scan rate of 2 mV s−1 for the fabricated MSCs and their excellent stability even after 50000 successive charge-discharge cycles by constant current. Most notably, the electrochemical impedance spectroscopy results revealed that the MSCs exhibited very fast response and close-to-ideal capacitive behavior even at around 1000 Hz. Specifically, the phase angle and specific capacitance measured at 120 Hz were −81.2 deg and 65.2 μF cm−2, respectively, in addition to a cut-off frequency of 3486 Hz at which the impedance angle is −45 deg. The device was tested as the capacitive energy storage component in a standard AC line filter, and its performance was found comparable to a commercial off-the-shelf aluminum electrolytic capacitor.